Method of treating oils



` April 6,

v. J. umv I2,316,092

METHOD OF TREATING OILS Filed Sept. 19, l942- |000 SOO 600 700 TORNEY Patented Apr. 6,

UNITED STATES PATENT IOFFICE Ma'rnon or mame oms Vernon J. Loyd, East Chicago, Ind., assignor to` v, Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York applicati@ september 19, 194z,'sem1 No. 458,953A 8 Claims. :,iCl. 196-.31).

This application is a continuation 'in partof l my prior application Ser.'No. 404,835, illed July f duction oi' the mercaptan contentJ of hydrocarbon fractions of the nature of gasoline and the like.v It has both the aspect oi a process which sweetens by conversion to innocuous compounds and of a process which can reduce themercapl 31, 1941. The invention has to do withthe retan sulfur content by actual removal ofthe mercaptans. o

In treating hydrocarbons, such as straight run gasoline, natural gasoline, cracked gasoline and the like, to 'render them sweet to the "doctor test, the objective is to remove materials of the I nature of dissolvedV sulfur. hydrogenfsulphide, mercaptans or the like or to convert them' tooin-` nocuous compounds. y Washing with aqueous solutions of strong alkalies, such as caustic soda will remove most ofthe hydrogen sulphide and sometbut not all, of the mercaptans. Washing with aqueous caustic to which some material has been added as a solutizer," or solubility promoter. enables the caustic to dissolve and remove more or al1 'of the mercaptans. Butylene glycols, butyric acids, and phenolic materials are so used. Olderfmethods make use of sodium plumbite formed by dissolving litharge in caustic soda,

` provision `of a novel process capable of reducing i mercaptan sulfur in petroleum hydrocarbons l and` which in one aspect of its use provides an internally regenerated treating method effective inrendering petroleum hydrocarbons sweet to the doctor test. o l,

.This invention is based upon the discovery that eiective reduction of mercaptan sulfur may I"be eiected by treatment with aqueous caustic soda solution containing tannic acid and that if, in addition to this, oxygen oran oxygen containing gas'be present, during the contacting of the oil and of such reagent, a sweetening type of reaction may be accomplished.

- The tannic acid when added to the usual strong caustic solution appears to be capable of 4exercisingor of controlling two functions. In

the flrst place, it exerts a "solutizer" type of` action in 4enhancing the capability of the caustic soda for the solution of mercaptans of higher molecular weight. This action is quite marked for mercaptans of ilve carbon atoms and higher,

and is apparently of little importance/for mer-` captans of lower molecular weight. The second function is apparently that of promoting greatly the oxidation of mercaptans to disulphides when -oxygen .or oxygen containing gases are present in vthe treating zone wherein the caustic tannin solution isl contacted with the oil. fraction.`

The caustic alkali solution to be used may be any of the usual alkaline solutions normally used for these purposes, such as caustic soda, caustic potash, alkali metal carbonates, ammonia and basic ammonium compounds and the like. Usual preference is 'had for caustic soda, in aqueous solutions of from about 5 Baum to 20 Baume, the usual and preferred strength being around 10 Baume.

. the eiIect here being to convert mercaptans to The tannic acid used may be the usual commercial grade of the material. l

I have found this tannic acid activator to be eective in quite small amounts, ranging from 5.0% downward to fractions of 1% with amounts of from abou 0.3% to about 1.0%, by weight ofv best'to caustic wash the oil, prior to this treatment, as with an aqueous alkaline reagent, to

remove hydrogen sulphide and the more readily` removable sulfur containing materials.

The following experimental data show the effectiveness of the process herein described. To

secure this data. straight run and cracked gasolines were treated with various caustic alkali TABLE I Effect' of taunic acid ou removal of inercaptan sufur from straight. run gasoline by caustic solution (Raw S. R. gasoline 0.005% RSII) Tannic Tempera- Ratio A Gas Extrac- Mercaptan NaOH kind'B. acid ture (NaOH: etmostions (numremoval (per cent) (F.) gaso.) phere ber oi) (percent) 0.3 100 1:4 l 72.5 1.0 100 1:4 1 72.5 5.0 100 1:4 1 67.5. 0.0 o 1:4 1 25,0 1.o 82 1:4 s 75.0 0.0 9o 1:4 1 29.0 0.o 9o 1:4 1 29.0 1.0 90' y1:4 1 31.8 1.o no 1:4 1 'f3.4 5.o 9o 1:4 1 o2. 5

v TABLE H Ecct of tanmc acid on removal of mercaptan sulfur from cracked gasoline by caustic solution (Thermal crackedgasoline 0.025% RSE) -Tannic TemperalRatio Ga's Extra@ Mei-captan' NaOH kind B. ac ure (NaOH: atmostions (numremoval (per cent) (F.) gaso.) pherc ber of) (percent) 0.0 100 1:4 1 59.0 0.3 100 1:4 1 77.3 1.0 100 1:4 l 81.8 0. 0 95 1:4 1 60. 2 1.0 95 '1:4 1 70.4 1.0 95 1,:4 1 87.1 1.0 95 1:4 l 58.1 1.0 95 1:4 3 85.3 0.0' 90 1:4 1 66.6 1.0 90- 1:4 1 67.4 1.o co 1:4 1 89.0 0.0 so 1:4 1 65.3 1.0 90 1:4 1 `83.6 0.0 90 1:4. 1 ,63.1 .1.0 90 1:4 1 88.2

l NaOH solu. boiled before using. a Ditto.

The above data demonstrates the effectiveness of the reagent as a promoter of the oxidation of mercaptans under the circumstances shown. Note particularly-those experiments wherein air was present in a caustic tannin solution as contrasted with those where air was present in a -caustic solution treatment utilizing caustic of the same strength and free from tannin. For example, in the first four horizontal lines oi Table I, the rst three show caustic tannin in the presv ence of air andthe ourth shows caustic alone in the presence of air. .In the first three the mercaptan removal is around 70%, in the fourth it is around Similar contrasts occur in Table H, particularly inthe rst and last experiments performed with 11 Baum caustic, the rst being` caustic alone in the presence of oxygen and ei'ecting a mercaptan removal of about 67%, the last being caustic tannin in the presence of oxygen rive at equilibrium.

and effecting a mercaptan removal to the extent Another aspect of the use of causticftannln reagents is shown by the drawing attached hereto.

lThe single figure of this drawingl shows the en-A hanced capability of caustic tannin solution for mere removal, as contrasted with oxidation,l o f certain mercaptans. This gure presents the distribution coecient' plotted against the number of carbon atoms contained in the mercaptans and was arrived at by treating a completely sulfur free light naphtha cut to various portions of which known amounts of known mercaptans had been added, comparative treats being made with and without tannin present in a caustic solution of the same. strength of caustic. The value plotted at the left hand in this drawing is Kq, the distribution coefficient. This distribution coecient is a figurearrived at by dividing the concentration of the mercaptan in the treating so- This is of particular interest, since it has always been these more dicultly removable high molecular weight mercaptans which have lowered the emciency of attempts to remove sulfur compounds by caustic soiutions.

Turning back to Table I above, wherein a cracked gasoline was treated, we nd certain experiments recorded which `confirm this removal. For example, considering operations with 11 Baume caustic, we find that using caustic without tannin, the same mercaptan removal was eiected whether oxygen ornitrogen was used, namely, 29%.. However, when 1% oi' tannin was added and nitrogen' was used, the

oxygen effect spoken of hereinabove lnot being present, the mercaptan removal was raised to 31.8%, an increase of approximately 10%.

Turning to Table II, and remembering that we have previously found thatcausticsolution in the absence of tannin gave about the same results, whether oxygen was present or not, we nd in the rst example, wherein 11 Baum caustic was used, but tannin was not present, a mercaptan removal of 66.6%. In the line just below where 1% of tannin was used in the caustic solution, the atmosphere was nitrogen and the oxidation effect was not present, we still nd an increase in mercaptan removal to 67.4%. The two increases in percentage of total mercaptan removal above, are relatively small, and in early work upon this discovery their significance was not understood. In view of later work resulting in the discovery of the effective solutizer action.

of tannicv acid in caustic solutions, it is now realized that in these two examples, the difference between results was actually indicative of a materially increased capability of the reagent. The capability was small in the case of the cracked gasoline treated in Table 1I because of the rather high percentage of mercaptans present therein, practically all were necessarily low molecular weight mercaptans whose solubility in caustic was pr-actically the same in either experiment. UHowever, in Table I, where a straight run gasoline vcontaining a greater amount of high molecular weight mercaptans was treated a more pronounced difference was obtained. In connec- :n

1. That method of removing mercaptans of l or more carbon atoms from petroleum fractions comprising contacting the fraction' with an aqueous alkaline reagent to which tannic acid has been added to promote the solution of mercaptans in said reagent.

2. That method oi removing mercaptans of 4 or more carbon atoms from gasoline and the like comprising contacting the oil with an aqueous solution of caustic soda activated by the addition of a small amount of tannic acid to promote the l solution of mercaptans in said caustic soda.

3. That method of removing mercaptans of 4 or more carbon atoms from gasoline and the like comprising contacting the oil with an aqueous solution of caustic soda activated by the addition of a small amount, less than about 5%, of tannic acid, to promote the solution of mercaptans in said caustic soda.

4. That method of removing mercaptans of 4 or more carbon atoms from gasoline and the like comprising contacting the oil with an aqueous solution of caustic soda activated by the addition oi' a small lamount, from about 0.3% to about 1.0%, of tannic acid, to promote the solution'of mercaptans in said caustic soda.

5. That method of removing mercaptan sulfur .of 4 or more carbon atoms from a light petroleum fraction, which consists of contacting the fraction with an aqueous lalkaline reagent to which tannic acid has been added to promote the solution of mercaptan sulfur in said reagent.

6. That method of removing mercaptan sulfurof 4 or more carbon atoms from a gasoline fraction, which consists of contacting the fraction with an aqueous solution of caustic soda activated by the addition of a small amount of tannic acid to promote the solution of mercaptan sulfur in said caustic soda.

7. That method of removing mercaptan sulfur of 4 or more carbon atoms from a gasoline fraction which consists of contacting the fraction with an aqueous solution of caustic soda activated by the addition of a small amount, less than about 5%, of tannic -acid to promote the solution of mercaptan sulfur in'said caustic soda.

8. That method of removing mercaptan sulfur of 4 or more carbon atoms from a gasoline fraction which consists of contacting the fraction f. with an aqueous solution of caustic soda activated by the addition of a small amount, from about 0.3% to about 1.0%, of tannic `acid to n promote the solution of mercaptan sulfur in said caustic soda.

VERNON J. LOYD. 

